On 06/21/2016 09:50 AM, James Greenhalgh wrote:
Hi,
This patch clears up the cost model for noce_try_cmove_arith. We lose
the "??? FIXME: Magic number 5" comment, and gain a more realistic cost
model for if-converting memory accesses.
This is the patch that has the chance to cause the largest behavioural
changes for most targets - the current heuristic does not take in to
consideration the cost of a conditional move - once we add that the cost
of the converted sequence often looks higher than we allowed before.
I think that missing the cost of the conditional move from these sequences
is not a good idea, and that the cost model should rely on the target giving
back good information. A target that finds tests failing after this patch
should consider either reducing the cost of a conditional move sequence, or
increasing TARGET_MAX_NOCE_IFCVT_SEQ_COST.
As this ups the cost of if-convert dramatically, I've used the new
parameters to ensure that the tests in the testsuite continue to pass on
all targets.
Bootstrapped in series on aarch64 and x86-64.
OK?
Thanks,
James
---
gcc/
2016-06-21 James Greenhalgh <james.greenha...@arm.com>
* ifcvt.c (noce_try_cmove_arith): Check costs after constructing
new sequence.
gcc/testsuite/
2016-06-21 James Greenhalgh <james.greenha...@arm.com>
* gcc.dg/ifcvt-2.c: Use parameter to guide if-conversion heuristics.
* gcc.dg/ifcvt-3.c: Use parameter to guide if-conversion heuristics.
* gcc.dg/pr68435.c: Use parameter to guide if-conversion heuristics.
LGTM as well. And yes, the cost of the cmove needs to be accounted for.
Thanks for doing something sensible on those tests. I would support
similar tweaks if we find others after installing this series.
jeff
